From mboxrd@z Thu Jan 1 00:00:00 1970 From: b29396@freescale.com (Dong Aisheng) Date: Mon, 4 May 2015 16:35:51 +0800 Subject: [PATCH RFC v1 2/5] clk: add missing lock when call clk_core_enable in clk_set_parent In-Reply-To: <55427D83.3060900@codeaurora.org> References: <1429107999-24413-1-git-send-email-aisheng.dong@freescale.com> <1429107999-24413-3-git-send-email-aisheng.dong@freescale.com> <55427D83.3060900@codeaurora.org> Message-ID: <20150504083549.GC4082@shlinux1.ap.freescale.net> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, Apr 30, 2015 at 12:07:47PM -0700, Stephen Boyd wrote: > On 04/15/15 07:26, Dong Aisheng wrote: > > clk_core_enable is executed without &enable_clock in clk_set_parent function. > > Adding it to avoid potential race condition issue. > > > > Fixes: 035a61c314eb ("clk: Make clk API return per-user struct clk instances") > > Cc: Mike Turquette > > Cc: Stephen Boyd > > Signed-off-by: Dong Aisheng > > --- > > Can you please describe the race condition? From what I can tell there > is not a race condition here and we've gone around on this part of the > code before to fix any race conditions. > Do you mean we do not need to acquire enable lock when execute clk_core_enable in set_parent function? Can you help explain a bit more why? The clk doc looks to me says the enable lock should be held across calls to the .enable, .disable and .is_enabled operations. And before the commit 035a61c314eb ("clk: Make clk API return per-user struct clk instances"), all the clk_enable/disable in set_parent() is executed with lock. A rough thinking of race condition is assuming Thread A calls clk_set_parent(x, y) while Thread B calls clk_enable(x), clock x is disabled but prepared initially, due to clk_core_enable in set_parent() is not executed with enable clock, the clk_core_enable may be reentrant during the locking time executed by B. Won't this be a race condition? Regards Dong Aisheng > -- > Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, > a Linux Foundation Collaborative Project >